At present, the recovery of discarded tires remains a serious problem, despite certain achievements in this field. Some discarded tires are utilized in civil engineering and in road construction, as well as in the manufacturing of different goods. Nevertheless about 30% of discarded tires, and in some countries, up to 80%, are still disposed in stockpiles. A large number of tires are located outside of the stockpiles, and pollute the environment. On the other hand the non-utilized discarded tires may present a valuable raw material being a source of chemical energy due to the organic and carbonized components contained in this material.
Most of the known methods for converting the rubber containing materials of tires into useful products are based on pyrolysis. A pyrolysis process generally operates at temperatures of about 500° C. in a low oxygen atmosphere and results in producing hydrogen-hydrocarbon gas, a liquid hydrocarbon product, and a solid material. The solid material comprises a carbonized part and the steel cord of the tire.
Many prior art reactors convert the rubber containing materials of tires into the aforementioned products by heat induced decomposition, but are impractical due to the resulting environmental pollution or due to cost ineffectiveness.
U.S. Pat. No. 4,240,587 discloses a vehicular processing plant for processing scrap tires and similar materials. The technical rubber is initially processed through a cryogenic crushing and separation section during which a considerable amount of reusable technical rubber is mechanically separated, and thereafter the remainder is pyrolytically treated so that reusable commercial byproducts are obtained while high-energy containing gases and oils are utilized in operation of the plant. This pyrolytic reactor is not economically viable as small scrap tire particles are fed thereto, resulting in high pre-processing costs.
U.S. Pat. No. 5,095,040 discloses a process for converting scrap tires into oil and carbon by shredding the tires to rubber crumb particles smaller than ¾ inch in size, charging the rubber crumb particles into an inclined heated rotating tube and maintained at a slight pressure above atmospheric pressure so as to minimize air infiltration into the tube, rapidly heating the rubber crumb particles to a temperature at which they decompose into a gaseous product and a solid residue, condensing a portion of the gaseous product, and recovering a liquid condensate from the condensed gaseous product. This process is also not cost effective due to the high pre-processing costs involved in shredding the tires to small pieces.
U.S. Pat. No. 5,225,044 discloses a rotary continuous pyrolytic conversion system for solid hydrocarbon based comminuted feedstock pieces. An oven chamber defined by a casing around an outer air-tight stationary drum in which is contained a rotatable converter drum heated by combustion products from a burner. Fins extending into the oven chamber from the stationary outer drum induce turbulence of the combustion products, increasing heat transfer from the combustion products to the outer drum, and thence to the converter chamber. A rod extends into the injection end of the converter drum for supporting scrapers against the inner periphery of the converter drum. A crusher bar is carried in the drum at the discharge end thereof and crushes the solid products which consist of char, metals and other non-organic materials. A chute containing water receives the pulverized discharge product and balances the pressure in the converter to maintain an air-tight seal therein. A second pyrolytic reactor may receive the solid pyrolysis products and be operative at a higher temperature than the first converter to destroy chlorinated hydrocarbons. In addition to the relatively high costs involved in comminuting the feedstock pieces, an additional disadvantage of this system is that the combustion products flow across the exterior of the outer drum and indirectly transfer heat to the converter drum only by convection, while the wall of the converter drum transfers heat to the feedstock pieces only by conduction.
It is an object of the present invention to increase the intensity of heat transfer to the feedstock pieces introduced to a reactor and to thereby increase the rate of pyrolysis by introducing heat carrier gases into a selected region of the reactor interior.
It is an additional object of the present invention to provide a pyrolytic reactor suitable for pyrolyzing relatively large feedstock pieces having a size greater than approximately 200 mm, thereby significantly reducing the pre-processing costs associated with prior art reactors.
It is an additional object of the present invention to provide a pyrolytic reactor for generating gas, and preferably liquid, products that are usable in industrial processes such as electrical energy generation.
It is an additional object of the present invention to provide a pyrolytic reactor that prevents, during the course of operation, products of pyrolysis from escaping therefrom to the atmosphere and to thereby prevent environmental pollution.
It is yet additional object of the present invention to provide a pyrolytic reactor that facilitates removal of the solid residue of a pyrolysis process without having to cease operation of the reactor.